| 摘要 |
PROBLEM TO BE SOLVED: To provide a preceding standby pump improved to be resistant to hunting caused by fluctuation in water level. SOLUTION: The preceding standby pump includes a passage 21 for mixing gas and water having one end 21a opened upstream in a fluid flow direction of a portion where an impeller 11 is housed in a pump casing 3, and the other end 21b opened to the inside of a suction water tank 2. In the pump, the passage 21 is formed into a conduit which has as a whole a shape of an approximately inverted-U and includes a fold-back part 21c folded back at a position higher than the highest water level HWL set in the suction water tank 2 and formed between one end 21a and the other end 21b. The passage 21 is provided with a suction structure part A including a U-shaped pipe 23 of which one end 23a is connected to a portion of the passage 21 between the up- and down-stream of the fold-back part 21c and the other end 21b, and of which the other end 23b is opened to the atmosphere. COPYRIGHT: (C)2011,JPO&INPIT
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